1. Field of the Disclosure
The present disclosure relates in general to a clock, and more specifically to a temperature-compensated high accuracy internal clock.
2. Description of the Related Art
In computer processing systems, internal clocks can be used to eliminate the need for expensive crystals, but require tighter temperature drift and resolution to communicate with external peripherals or devices. Another requirement for internal clocks is the ability to tune to another more accurate source or “clock recover” to communicate with external peripherals. Other considerations for external communication include cycle to cycle jitter and time interval error.
Requirements vary depending upon how the clock is used, but usually there are incremental requirements that need to be met for each use. For example, for a full speed Universal Serial Bus (USB) peripheral device, a clock that is within 2500 parts per million (ppm) of an integer multiple of 12 or 48 Mhz is adequate. Alternatively, a clock that is within 15000 ppm (1.5%) and can be quickly tuned to the incoming USB data stream to 2500 ppm is considered adequate.
Thus, it is desirable to provide processing systems with clocks that generate signals well within frequency accuracy specifications.